Checking Fuel Pressure: Ram Cummins Maintenance Guide

The Cummins 5.9-liter, 12-valve engine is a large diesel engine that was the stock engine for the Dodge Ram pickup during the 1990s and 2000s. If you're experiencing fuel-related problems, you can run a fuel-pressure test to isolate them. These engines come equipped with an easy-access test port, referred to by some as a Schrader valve. To check your fuel pressure, you can screw a fuel-pressure gauge directly onto this port for testing.

First, pop the hood on the Dodge Ram and locate the test port on the left-hand front side of the engine compartment. Unscrew the valve cap and pull it back, then screw the end of the fuel-pressure gauge onto the test port. Start the car and allow it to run for around five minutes. Examine the fuel-pressure reading. If it still appears to be fluctuating, give it a few more minutes until the level peaks out. The pressure should read between 15 to 18 psi.

Turn the motor off and remove the pressure gauge from the test port. Wipe up any spilled fuel with an old towel and replace the test port cap.

The Schrader valve on the back of the fuel filter housing

The Schrader valve, also known as the test port, is located on the back of the fuel filter housing. It is easily accessible and can be found on the left-hand front side of the engine compartment. To check the fuel pressure, simply unscrew the valve cap and pull it back. Then, screw the end of the fuel pressure gauge onto the Schrader valve.

Once the gauge is securely attached, start the engine and let it run for about five minutes. During this time, observe the fuel pressure reading on the gauge. If the reading is fluctuating, allow the engine to run for a few more minutes until the pressure levels out. For a 5.9-liter 12-valve Cummins engine, the fuel pressure should ideally be between 15 to 18 psi.

It is important to ensure that you have an appropriate fuel pressure gauge that can read up to 30 psi. Additionally, always exercise caution when working with fuel and use an old towel to wipe up any spilled fuel.

By regularly checking the fuel pressure with the Schrader valve on the back of the fuel filter housing, you can ensure the optimal performance of your Ram Cummins engine and identify any potential fuel-related issues.

A tapped banjo bolt plumbed into the CP3 pump

When installing a tapped banjo bolt, it is important to ensure the correct thread size and type of fitting. Some common thread sizes mentioned for the CP3 pump inlet are M12 and M14. There are also different types of fittings available, such as push-lock couplings and AN fittings. It is recommended to use a rubber fuel hose when installing the gauge to help stabilise the reading.

It is worth noting that some people choose to purchase a new banjo bolt instead of drilling and tapping the factory bolt. This is a fairly inexpensive option and can ensure a proper fit. Additionally, a rubber fuel hose can be attached to the banjo bolt before installing the gauge to help stabilise the reading and reduce vibrations.

Overall, a tapped banjo bolt plumbed into the CP3 pump provides a convenient way to monitor fuel pressure and can help identify potential issues with the fuel system.

The top of the fuel filter housing

To check the fuel pressure, first, open the hood of your Dodge Ram and locate the Schrader valve. Unscrew the valve cap and pull it back, then screw the end of the fuel pressure gauge onto the valve. Start the engine and let it run for about five minutes. Check the fuel pressure reading—if it's still fluctuating, wait a few more minutes until it peaks out. The pressure should be between 15 to 18 psi.

Turn off the engine and remove the pressure gauge from the Schrader valve. Wipe up any spilled fuel with an old towel, then replace the valve cap.

It is important to monitor your fuel pressure to ensure the health of your engine and to catch any potential issues early on. By regularly checking your fuel pressure and keeping it within the optimal range, you can help maintain the performance and longevity of your Ram Cummins engine.

The side of the CP3 pump

The CP3 pump is a high-pressure fuel pump found on the common rail Cummins engines, such as the 5.9L and 6.7L. It is driven by the timing belt at a 1:1 ratio to the crankshaft and is responsible for supplying fuel at high pressure to the fuel rail and injectors. The CP3 pump can generate fuel pressure between 4351-23,206 psi, with a minimum of 1500 psi required for the engine to fire during cranking.

The CP3 pump has a gearotor supply pump attached to its rear, which is driven by the end of the high-pressure pump shaft. This medium-pressure fuel pump draws fuel from the lift pump in the fuel tank and supplies it to the high-pressure injection pump. The outlet of the gearotor pump also provides pressurized fuel to the Fuel Control Actuator (FCA) solenoid valve and the Cascade Overflow Valve, which regulates internal housing pressure.

The FCA solenoid is controlled by the Engine Control Module (ECM) and meters the amount of fuel flowing into the high-pressure elements inside the high-pressure pump. It is inactive for up to 30 seconds after the ignition is turned on to allow maximum fuel pressure during cranking and start-up. The ECM then assumes control of the FCA valve when crankshaft position and rail pressure are within acceptable limits.

By checking the fuel pressure on the side of the CP3 pump, you can gain valuable insights into the health of the fuel system. Low fuel pressure at idle or significant drops in pressure during acceleration can indicate issues with the lift pump or fuel filter. Upgrading the lift pump and adding additional fuel filters can help improve fuel pressure and overall engine performance.

The test port on the left-hand front side of the engine compartment

To check the fuel pressure on a 5.9 12V Cummins engine, you must locate the test port on the left-hand front side of the engine compartment. This test port is also referred to as a Schrader valve, and it provides easy access for testing fuel pressure.

Firstly, pop the hood on the Dodge Ram and locate the test port. Unscrew the valve cap and pull it back, then screw the end of the fuel pressure gauge onto the test port.

Next, start the engine and allow it to run for around five minutes. Examine the fuel pressure reading. If the reading is still fluctuating, let the engine run for a few more minutes until the level peaks out. The pressure should ideally read between 15 to 18 psi.

Once you have recorded the reading, turn the motor off and remove the pressure gauge from the test port. Use an old towel to wipe up any spilled fuel, and remember to replace the test port cap.

This process will allow you to effectively check the fuel pressure on your Cummins engine and identify any potential fuel-related issues.

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